If open file dialog is a native one, setting the layout will do more harm
than good. Specifically, on Windows with Qt 5 the dialog becomes completely
unusable.
This has a couple of benefits: 1) it is clearly visible to the user that
the list is filtered (doesn't display all the torrents) even when filter
bar is hidden, 2) doesn't lead to filter bar controls being shifted to
the left/right as when "Show:" label text changes.
Disable "Open Folder" and "Verify Local Data" actions for magnets in
Torrent menu. If more than one torrent is selected, "Verify Local Data"
is enabled but only non-magnets are verified if activated.
Add a few sanity checks when opening folder, just in case.
We don't currently (if ever) provide context help, so the button is
useless. Moreover, on Windows 10 it's even larger than before and
sometimes title text doesn't fit because of it.
Since double-click is usually used to open things, don't use it to enter
edit mode, use platform-specific keyboard shortcut instead (Return, F2,
etc).
Add context menu duplicating available actions, resembling that of Mac
client. This includes new "only check selected" action.
Speed up DND/priority change for large numbers of files at once. Make
DND/priority toggling more natural: if both parent and its child are
selected, only act on parent (with all its children following).
Use simple tokenization instead of splitting the file path into
QStringList for each item. Don't expand each added item separetely
during population/update. Don't expand all the items but just up to the
point where parent has more than one expandable child.
Also, fix items order by sorting items after population/update. Fix
sorting by size on systems where uint64_t != quint64.
Simplify DND checkboxes drawing, this also fixes incorrect drawing on
Mac when file tree widget is inactive.
Do better job calculating column widths for file tree to avoid ellipsis.
Fix file tree sorting order for size and priority columns.
Change key to toggle priorities to Shift+Space instead of Enter/Return
to avoid conflicts with name editing and default button handling.
Fix selected tracker item background drawing in certain cases.
Split FileTree.{h,cc} and FilterBar.{h,cc} files so that each class
is in its own file.
This breaks translations (some classes got renamed => context changed),
to be fixed by next commit (along with Tx sync).
